1. Field of the Invention
The present invention relates to plasma processing apparatuses. In particular, the invention relates to a plasma processing apparatus such as etching, film deposition and ashing apparatuses used for the process of manufacturing a semiconductor device, liquid crystal display or solar cell for example.
2. Description of the Background Art
With increase in size of a substrate used for manufacturing a semiconductor device, LCD (liquid crystal display) or the like, plasma processing apparatuses have recently been developed for processing such a substrate with a large area. Apparatuses are developed particularly for LCD to process a substrate of 1 mxc3x971 m or greater in size. These apparatuses address a challenge of making plasma uniform A challenge to be addressed by those apparatuses developed for film deposition, etching and ashing for example is improvement of the plasma processing rate for enhancement of the throughput of the apparatuses. A challenge for a dry etching apparatus is to control the cross sectional shape produced by etching in order to meet the increasingly reduced size of the pattern as well as the increased number of layers.
A microwave plasma processing apparatus with the purpose of ensuring uniform plasma is disclosed for example in Japanese Utility Model Laying-Open No. 4-117437 according to which a metal plate having slits is provided between an air layer under a microwave line of dielectric and a second dielectric to adjust the intensity distribution of microwave and accordingly achieve a uniform plasma density in a plasma generating chamber.
The plate for this apparatus is thick in consideration of deformation. However, the thick plate causes an abnormal discharge on the edge of the central portion of a microwave guide chamber. When a thinner plate is used, the metal and dielectric cannot be brought into contact with each other due to large thermal expansion coefficients of the metal and dielectric and an abnormal discharge could occur. These problems are indicated in Japanese Patent Laying-Open No. 2000-91097 which discloses its invention to overcome the problems.
FIG. 9 shows a structure employed by the invention disclosed in Japanese Patent Laying-Open No. 2000-91097, including a microwave dispersion plate 65 made of Al (aluminum) with a thickness in a range from 0.2 mm to 2 mm. Specifically, referring to FIG. 9, microwave is transmitted from a microwave generator 61 to be passed through a waveguide 62, a dielectric line 63, an air layer, a first dielectric 64, microwave dispersion plate 65, a second dielectric 66, and a third dielectric 67 to supply energy to a processing chamber 68. This structure provides a uniform ashing.
It is a known technique to apply, to a material to be processed, a bias voltage of DC, AC or pulse in order to control the amount of plasma ion irradiation and thus control the processing rate or the cross sectional shape of an etched film. A method of applying a bias voltage to a material to be processed is disclosed for example in Japanese Patent Laying-Open No. 2000-68227 according to which a porous electrode fixed at a ground or positive potential is provided to face a plane of the material to be processed with a space therebetween, so that a pulse or DC bias voltage is applied to the material.
Although Japanese Utility Model Laying-Open No. 4-117437 and Japanese Patent Laying-Open No. 2000-91097 show the technique of using a dispersion plate for rendering microwave uniform, no method of designing the dispersion plate is disclosed. In addition, although application of a high-frequency bias voltage to a sample stage is disclosed, the third dielectric 67 shown in FIG. 9 opposite a substrate 71 is made of ceramic so that the potential of the third dielectric 67 cannot be adjusted. Therefore, an efficient application of the bias voltage to substrate 71 is impossible and thus a problem arises that an adjustable range of ion irradiation energy to a material to be processed cannot be expanded
According to a technique in an embodiment of Japanese Patent Laying-Open No. 2000-68227, an ICP (inductively coupled plasma) apparatus is used with a plasma source which is an RF (radio frequency) power source on the order of MHz in frequency, and thus nothing is described about generation of plasma by means of a microwave power source. Accordingly, no problem is described that arises due to the shorter wavelength of microwave than the length of a vacuum device with one side of approximately several hundreds mm to 1000 mm (for f=2.45 GHz, free-space wavelength in vacuum is 122 mm). In other words, there is disclosed no design to address the problem concerning the standing wave distribution of microwave when plasma is excited.
For a microwave-excited plasma processing apparatus, a microwave circuit should be regarded as a resonator and a portion where microwave enters a vacuum chamber constitutes a part of the resonator. Then a design should be made in consideration of propagation characteristics of the microwave regarding the microwave entrance portion, in terms of start and maintenance of plasma discharge by a low power as well as plasma uniformity. However, the publications referred to above provide no guideline for making such a design.
One object of the present invention is to provide a plasma processing apparatus using microwave to excite plasma, with easily-adjustable ion irradiation energy directed to a material to be processed as well as uniform plasma processing of the material within its plane.
According to the present invention, the plasma processing apparatus includes a process chamber for processing by means of plasma, a microwave transmission unit for transmitting microwave to the process chamber, a dielectric for radiating the microwave transmitted by the microwave transmission unit into the process chamber, and a slot antenna plate formed of conductor, placed on a side, facing the process chamber, of the dielectric, and including an opening for passing the microwave there through radiated from the dielectric.
The plasma processing apparatus of the present invention includes the slot antenna made of conductor, the slot antenna being placed on the side of the dielectric that faces the process chamber, and thus the potential of the slot antenna plate can readily be adjusted. Then, the potential of the slot antenna plate can be adjusted to control the direction of plasma ions for example with respect to a substrate being processed (bias effect). For example, plasma ions can be made incident on the entire surface of the substrate substantially perpendicularly thereto by adjusting the potential of the slot antenna plate at a ground potential and applying a bias voltage to the substrate. A material can thus be plasma-processed uniformly within its plane.
Moreover, the slot antenna plate can be made contact with the dielectric to shorten a space wavelength of microwave compared with that when an air layer is present between the slot antenna plate and dielectric. Consequently, the intervals between openings of the slot antenna plate can be shortened so that a greater number of openings are formed. The microwave radiated into the process chamber through the openings can thus be distributed uniformly in the process chamber.
In addition, a plurality of openings with their positions and dimensions appropriately defined for the standing wave of microwave can provide efficient and uniform radiation of the microwave into the process chamber.
Preferably, for the plasma processing apparatus described above, the opening of the slot antenna plate is positioned directly below an antinode of a standing wave of the microwave in a resonator constituted of the microwave transmission unit and the dielectric.
The magnetic field directly below the antinode of the standing wave is greater. Then, the opening is positioned directly below the antinode of the standing wave to allow current to be induced around the opening, this current inducing a magnetic field from the opening. In other words, an efficient radiation of the microwave into the process chamber is achieved by placing the opening directly below the antinode of the standing wave.
Preferably, for the above-described plasma processing apparatus, the slot antenna plate has its potential adjusted at a ground potential or a positive potential.
The potential adjustment of the slot antenna plate makes it possible to control the direction of plasma ions for example with respect to a substrate to be processed.
Preferably, for the above-described plasma processing apparatus, the slot antenna plate includes a channel for a process gas.
In this way, control of the process gas flow is facilitated so that a material to be processed can uniformly be processed with plasma.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.